The temperature of different parts in a flame

We had a laboration where we did some temperature measurments on a flame and wrote a report on this. We got it back and were told to explain more deeply why we had a temperature maximum at a certain point.

What happend was this. We started to meassure on the point located preciecly above the blue part of the flame. Then we stepped out to the side with steps of 1mm. At 7-8mm we reached a temperature maximum. How can I expalin what happend there? One theory is that I can just blame the thermal-elements we used and say that we did an inaccurate meassurment. But I'm not really sure that would do the trick. Got some wounderings about perhaps it has something to do with that we have the best methan-oxygen mix there (we had an methan oxygen flame)